Based on what I've heard and seen; sure, the monitors could be left on 24/7 and survive. But a lot of the Sanyo/Nintendo monitors would need minor repairs from faulty parts. It reduced the life of the monitor, sure; but if the game was making money an operator usually kept a spare monitor to toss in the game when the one would euventually fail.

Laundromats are a horrible environment for a game; and I saw many games fail as a result of excess dust and carbon built up in the monitor; those flybacks would get hot, crack, and boom. I know this because I used to service games in a laundromat. Not only do they get physically torn up (you wouldn't belive how much people just assume they can destoy the arcade games); but the dust is really bad for them.

Back in the 80's that stuff wasn't a huge problem (save for some Nintendo and Atari Vectors); they ran them till they died, even if it was 24/7 for a couple years. Some of the guys that fixed the things got to know exactly what parts needed to be changed and could often do it while the chassis was still in the machine. Of course by the time I got to the industry; age had just taken it's toll on these things. Chassis were failing left and right due to old caps; flybacks were stressed and blowing up.

Modern arcade games are usually garbage, both game-wise and to work on. It's just the same re-hashed idea after rehashed idea; all running on a standard PC that's probably two or three generations older than the one on your desk and vastly inferior to the gaming consoles out now.